Related Art 1
Conventionally, there has been disclosed a method of detecting both a current flowing to a parallel connector coupled to a positive electrode side and a current flowing to a parallel connector coupled to a negative electrode side in a DC power supply of one arm, thereby detecting an output current (see e.g., Patent Document 1).
FIG. 4 is a schematic diagram showing a current detecting circuit of an inverter device according to a first related art.
In FIG. 4, numerals 61 to 66 denote parallel connectors constituted by semiconductor switching elements 11 to 16 and diodes 21 to 26, respectively. The diodes 21 to 26 are coupled in parallel with the semiconductor switching elements in reverse directions. Numerals 31 to 34 denote current detecting resistors. Numerals 41 to 44 denote amplifiers for amplifying voltages across the current detecting resistors respectively. Numeral 50 denotes an electric load coupled to output terminals U, V and W of each arm. P denotes a positive electrode of a DC bus of an inverter, and N denotes a negative electrode.
Moreover, Numeral 67 denotes an U arm, numeral 68 denotes a V arm and numeral 69 denotes a W arm, and each of the arms has two parallel connectors connected in series. Furthermore, the U arm 67 includes the current detector 31 and the current detector 32 between the positive electrode P and the parallel connector 61 and between the negative electrode N and the parallel connector 62 respectively. The W arm 69 includes the current detector 33 and the current detector 34 between the positive electrode P and the parallel connector 65 and between the negative electrode N and the parallel connector 66 respectively.
Next, an operation will be described.
FIGS. 5A to 5D are time charts to describe a current detecting operation according to the related art.
FIG. 5A shows an output current of a U phase. FIG. 5B shows a voltage across the current detecting resistor 31. FIG. 5C shows a voltage across the current detecting resistor 32.
By amplifying the voltages of the current detecting resistors 31 and 32 with the amplifiers 41 and 42 respectively and adding them with an amplifier (not shown), it is possible to obtain a current detecting signal of the U phase as shown in FIG. 5D.
More specifically, the output current of the U phase is detected by two current detecting resistors coupled to the U arm and an output current of a W phase is detected by two current detecting resistors coupled to the W arm.
Related Art 2
Moreover, there has been disclosed a method in which each arm of a three-phase inverter is provided with a current detector for detecting a current flowing to a parallel connector coupled to a negative electrode N side of a DC power supply. In this method, a current of a parallel connecting conductor on a negative electrode side of two phases having a shorter OFF time in a PWM control is simultaneously detected and set to be an output current of the inverter (see e.g., Patent Document 2).
FIG. 6 is a schematic diagram showing a current detecting circuit of an inverter device according to a second related art.
In FIG. 6, numerals 61 to 66 denote parallel connectors. Numerals 35 to 37 denote current detectors for detecting a current flowing to the parallel connectors coupled to a negative electrode N side of a DC power supply of each arm. Numeral 50 denotes an electric load coupled to an output. Numeral 71 denotes a detection phase selecting portion for selecting a detection phase. Numeral 72 denotes a current detecting portion for sampling a current detection value obtained by the selecting portion.
Next, an operation will be described.
FIG. 7 is an operational waveform diagram showing an operation according to the related art.
A carrier is compared with U-phase, V-phase and W-phase voltage commands respectively, and U-arm, V-arm and W-arm drive signals are generated. Currents flowing to the parallel connectors 62, 64 and 66 on the negative electrode N side of a U arm 67, a V arm 68 and a W arm 69 as shown in FIG. 6 are detected by the current detectors 35, 36 and 37 respectively and then are inputted to the detection phase selecting portion 71. The detection phase selecting portion 71 selects two phases having longer ON times of a semiconductor switching device on the negative electrode N side of a DC power supply and then inputs the two phases to the current detecting portion 72. The current detecting portion 71 simultaneously performs sampling on conducting currents of the selected two phases based on a sample timing signal and then sets them as output currents of the selected phases.    Patent Document 1: JP-A-2000-166247    Patent Document 2: JP-A-2003-79157